The present invention relates, in general, to a method of selective metallization of high temperature semiconductors to produce ohmic or rectifying contacts. More particularly, the invention relates to a method of modifying the surface of a high temperature semiconductor material and thereafter depositing metal on the modified surface by chemical vapor deposition to produce the required contact metallization.
High temperature semiconductors; that is, wide-band-gap semiconductors, are promising materials for blue lasers, high frequency, high-power devices, and for high temperature applications such as sensor circuits for automobile engines. However, the contact metallization for high temperature semiconductors must be able to withstand repeated cycling, have good adhesion, and must not react at high temperatures if the devices are to be successfully used. Refractory metals and refractory metal silicides should fulfill the criterion for low reactivity, but problems such as poor adhesion arise due to differences in the thermal properties of the metallization and the substrate.
A promising technique for depositing refractory metals and refractory metal silicides for VLSI applications is selective chemical vapor deposition (CVD). The advantages of this technique are that it will, typically, only deposit refractory metals and refractory metal silicides on silicon, germanium, or metals, but will not deposit these materials on oxides or insulators. Because of this feature, masking a silicon wafer with patterned silicon dioxide will allow the refractory metal or refractory metal silicide to be patterned during deposition. U.S. Pat. Nos. 4,746,621 and 4,907,066 to Thomas et al demonstrated a method for fabricating a multi-level interconnect system using tungsten CVD. In accordance with those patents, silicon was implanted in the bottom of trenches formed in a silicon dioxide layer and after etching the silicon dioxide to expose the implanted silicon, tungsten was deposited on the implanted material in the trenches to form an interconnect line. In this manner, selective CVD tungsten was deposited on silicon dioxide. However, there is also a need to deposit selective CVD metals and/or alloys onto high temperature, wide-band-gap semiconductors.